The conservation war appears to be over at the National Gallery of Art. The staff conservators have won.

In a move that seemed to call their competence into question, they were put "on hold" last June by gallery president Paul Mellon who ordered them to stop all "major treatment" of the Old Master pictures in the gallery's collection. Yesterday, however, they were told to carry on.

"They have been given a clean bill of health," said director J. Carter Brown.

The moratorium was lifted yesterday following a meeting of the gallery's trustees. A carefully worded statement noted that the board had "considered" the "findings" of the blue-ribbon panel of consultants it months ago invited to take a careful look at the conservation lab and had "expressed its confidence in the competence of the present conservation staff."

"The director called a meeting to tell us the good news," said Kay Silberfeld, the gallery's conservator of paintings. "Of course we were relieved."

Nine outside experts - among them scholars from Harvard and Williams, the directors of the Frick Collection and the Cleveland Museum of Art, the curator of paintings at Boston's Museum of Fine Arts, and the former chief conservator of New York's Metropolitan - had examined the techniques employed by Silberfeld and her colleagues.

"No member of the panel, chosen to reflect a broad spectum of viewpoints on conservation, found any evidence of physical harm to the gallery's paints," the trustees' statement said. "The survey revealed confidence in the integrity and professionalism of the gallery's conservation staff."

Brown was asked yesterday if some outside conservator would be placed in charge of the conservation staff. "There is no question of that," he said.

Although "The Mill" by Rembrandt was the most famous painting caught up in the crisi - it was being cleaned when the moratorium was declared - the controversy appears to have been sparked by another painting, one, ironically, that was cleaned in Oberlin, Ohio, rather than in the gallery's own lab in Washington.

"The Gerbier Family" by Rubens had been purchased by the gallery through Sir Geoffrey Agnew, the noted London dealer. Gallery staffers indicate that when Agnew saw the cleaned Rubens he complained to Mellon. Agnew left, with reason, that its color had been altered. Mrs. Gerbier's skirt, once brownish red, had become bright green.

Brown was asked yesterday whether that Rubens might be sent away for corrective restoration. "That could very well be," he said.

Agnew apparently convinced Mellon that excessively technological conservation had changed the picture's colors and that "European" methods that are more dependent on the eye of the conservator would have done less damage. Rather than attempt to resolve the issue by fiat, Mellon turned to outside specialists and declared the moratorium that was lifted yesterday.

The gallery's conservators received letters of support from colleagues who blamed the controversy on competition between the two schools of conservation. "It was political from the start," said one gallery employe. "They were fighting for a plum - the multi-million dollar lab in the new East Building."